The invention relates to a building drum for building an unvulcanized tyre or air spring using rubber components. The building drum comprises:
a central shaft with a circumferential wall having an outer diameter,                a casing with a circumferential surface for arranging the components thereon, wherein the casing comprises a substantially continuous opening having an inner diameter that corresponds with the outer diameter of the circumferential wall of the central shaft, wherein the casing is detachably attached to the central shaft.        
Such a building drum to be used in building an unvulcanized tyre using rubber tyre components, with reinforcement cords and two beads that may or may not be provided with a bead filling strip, is described in European patent 1.771.295. Said patent describes an assembly including tyre drum with turn-up mechanism, wherein the tyre drum is provided with a central shaft, wherein the assembly comprises at least two pairs of casings, wherein the first pair of casings is adapted to a first, smallest bead size of a first tyre and the second pair of casings is adapted to a second, larger bead size of a second tyre, wherein the pairs of tyres are arranged on the central shaft in an interchangeable manner.
The tyre building drum according to European patent 1.774.295 comprises a horizontal hollow shaft that is rotatable about a centre line, within which hollow shaft a spindle shaft is arranged, on which two sleeve-shaped nuts are arranged in a movable manner. Pins extend from the sleeve-shaped nuts in radial direction through axially oriented slits in the hollow shaft. On the pins a casing is attached, which as a result is axially movable with the nut at rotation of the spindle shaft.
Several casings are present in the assembly, wherein the other pairs of casings are substantially similarly shaped, at least having the same inner diameter. The other casings are prepared for a certain tyre dimension, through turn-up arms, bead clamping sections, bead inner supports etc. all adjusted thereto being mounting beforehand. When changing from manufacturing the one tyre size to the other tyre size, the casings are changed by at a free outer end of the drum, removing an end plate and also the compressed air connection, and uncoupling the pins of the casings on the central shaft. The casings can then be slid from the hollow shaft via the free outer end. Other casings for manufacturing tyres of another tyre size can be slid onto the hollow shaft via the free outer end, and be connected to the pins.
The casings being interchangeable on the one hand renders repair and maintenance of the casings relatively simple, also because said activities do not need to take place on the machine. On the other hand it ensures that a first set of casings for manufacturing tyres or air springs of a first type, can quite easily be replaced by another, second set of casings for manufacturing tyres or air springs of a second type that is different from the first type.
A building drum with an interchangeable casing is for instance known from U.S. Pat. No. 4,521,269. Said patent describes a building drum that is provided with a central shaft with a circumferential wall having an outer diameter, and with a casing with a circumferential surface for arranging the components thereon, wherein the casing comprises a substantially continuous opening having an inner diameter corresponding with the outer diameter of the circumferential wall of the central shaft, wherein the casing is detachably attached on the central shaft, and wherein the casing is provided with a coupling pin that is moveable from a coupled position in which the coupling pin extends in an opening in the circumferential wall of the central shaft, to an uncoupled position in which the coupling pin is placed outside of the circumferential wall of the central shaft.
However for the building drum to operate properly and to prevent damage, it is highly desirable that the casings are adequately and fixedly connected to the shaft, at least prior to the building drum becoming operational.